Processes for forming aldehyde products by the hydroformylation reaction of an olefinic compound with carbon monoxide and hydrogen in the presence of a rhodium-tertiary organophosphine complex hydroformylation catalyst are well known in the art. Of particular interest are those hydroformylation reactions designed to produce aldehydes at low pressures, such as disclosed, e.g. in U.S. Pat. Nos. 3,527,809; 4,148,830; 4,247,486; and 4,731,486.
Commercial experience has shown that, even in the substantial absence of extrinsic catalyst poisons, rhodium tertiary organophosphine complex catalysts lose activity (i.e. become partially deactivated) during the course of continued prolonged hydroformylation and such is commonly referred to as intrinsic deactivation. While it is difficult to ascertain the precise reasons for such loss in activity, such deactivation is believed to be due in a large part to the combined effects of a number of processing conditions, e.g. reaction temperature, reactant partial pressures, the phosphine ligand, the ligand to rhodium mole ratio, and rhodium concentration employed. Since the variables significant for such catalyst instability are also variables essential for the hydroformylation, obviously such deactivation can not be totally avoided although it can be controlled or minimized. However, eventually the activity of the catalyst will decrease to such a point that it is no longer desirable to operate the hydroformylation process and the catalyst will either have to be reactivated or discharged and replaced with fresh catalyst. Accordingly reactivation of such partially deactivated rhodium complex catalysts remains highly important to the state of the art in view of the high cost of rhodium as seen by the many various methods that have been proposed by the prior art for minimizing or preventing such deactivation and/or reactivating the partially deactivated rhodium complex hydroformylation catalyst.
For instance, U.S. Pat. No. 4,277,627 advocates that such deactivation can be reduced or substantially prevented by establishing, controlling and correlating the hydroformylation reaction conditions of temperature, carbon monoxide partial pressure and ligand to rhodium mole ratio to enhance stability of the catalyst via a stability factor formula.
U.S. Pat. No. 4,260,828 suggests utilizing the stability effect that alkyldiarylphosphine has on the rhodium catalyst and adjusting the reaction conditions to be more severe in order to regain the loss in catalyst productivity caused by such phosphine liquid.
U.S. Pat. No. 4,221,743 relates to a hydroformylation process wherein the rate of productivity of the process can be maintained at a desired rate by feeding oxygen during the hydroformylation reaction to the homogneous liquid phase composition of the reaction so as to maintain or increase the activity of the catalyst.
Japanese Patent Application Pub. No. 23,212/76 relates to maintaining or improving the rhodium catalytic activity of the hydroformylation reaction by removing the aldehyde from the reaction product mixture containing the catalyst and then treating all or a portion of the liquid catalyst medium with oxygen during recycle of the catalyst to the hydroformylation reaction. U.S. Pat. No. 4,041,082 relates to the same type of reactivation treatment save for employing carbon dioxide instead of oxygen.
U.S. Pat. No. 4,196,096 relates to a method for regenerating rhodium hydroformylation catalysts which comprises the steps of removing all or a portion of the inactive catalyst from the hydroformylation reaction, adjusting the aldehyde content so as to have at least one mole of aldehyde per mole of rhodium and ligand present and treating the catalyst with oxygen or an oxygen containing gas at a temperature below the boiling point of the aldehyde, removing any solid material formed during oxidation and adjusting the ligand to rhodium ratio as required for use in the hydroformylation reaction.
U.S. Pat. No. 4,605,780 advocates enhancing the activity of the rhodium complex hydroformylation catalyst by stopping the hydroformylation reaction and treating the catalyst containing hydroformylation reaction medium with oxygen to convert free alkyldiarylphosphine ligand to its corresponding phosphine oxide.
U.S. Pat. No. 4,297,239 advocates that partially deactivated rhodium tertiary organophosphine complex catalysts can be regenerated or reactivated by forming a rhodium complex concentrate via distillation of the hydroformylation reaction medium, followed by oxidation and/or washing of the concentrate if desired, said concentrate being employable as a source of reactivated rhodium for the catalyst of any hydroformylation process.
U.S. Pat. No. 3,555,098 suggests maintaining or improving the rhodium catalytic activity of a hydroformylation reaction by washing all or a portion of a liquid medium containing the catalyst with an aqueous solution, e.g. an aqueous alkaline solution to remove by product acid, e.g. carboxylic acid, formed during hydroformylation by oxidation of the aldehyde which may have been due to oxygen contamination of the reactant gas system.
U.S. Pat. No. 4,283,304 advocates improving the activity and increasing the life span of the rhodium complex catalyst of a continuous hydroformylation process (e.g. column 21) by removing in situ produced alkyldiarylphosphine ligand from the hydroformylation reaction medium by treating said medium with an alpha, beta unsaturated compound (as seen e.g. in column 10) such as a halide, carboxylic acid or anhydride of the carboxylic acid (e.g. vinyl chloride, maleic acid, and maleic anhydride, etc.), allowing an aqueous mixture of said treated medium to separate into two phases and separating the aqueous phase which contains the solubilized reaction products of the alkyldiarylphosphine present and said alpha, beta unsaturated compound from the non aqueous phase containing the rhodium complex catalyst, which non aqueous phase can be washed with any suitable aqueous alkaline solution e.g. sodium bicarbonate and water if desired. The non aqueous containing catalyst solution can then be reemployed in the hydroformylation process.
While all of the above prior art treatment procedures suggested to effect catalyst reactivity may have certain individual beneficial aspects, there is still a need in the art for a method which permits restoration of such partially deactivated rhodium catalyst activity under simple mild conditions and without complicated handling or processing procedures and without introducing unduly adverse side reactions.